Conventional lighting devices such as incandescent light bulbs are rather inefficient as lighting devices due to the amount of heat being released from the lamp. A majority of the electricity is transferred into heat. In some bulbs as much as 95-96% of the electricity is transferred into heat and the remaining 4-5% into light. In addition the incandescent lamp suffers from a relatively short life time of about a thousand hours.
Solutions using semi conductor based lighting devices have gain increased attention due to their energy efficient characteristic properties in which approximately 50% of the electricity is transferred into heat and approximately 50% into light. The semiconductor based light sources are also combined with a relatively long life time of tens of thousands of hours.
Whereas the incandescent light bulb emits light in all directions and achieves a homogeneous light distribution pattern, the semiconductor based lighting device has a directed light, which results in a non-uniform light distribution pattern.
One solution to the non-uniform light distribution pattern is disclosed in U.S. Pat. No. 7,229,196, which describes a lighting device having a light transmitting member in the shape of a toroid having a top and a bottom reflector. The light distribution pattern is improved by the light transmitting member, however the overall light distribution pattern does not resemble the light from an incandescent bulb.